六種有機溶劑之Tenax-TA 被動式採樣方法評估

Tenax-TA Passive Sampler Evaluation for Six Organic Solvents

本研究主要是以動態稀釋的方式產生對──二甲苯（p-Xylene）、苯乙烯（Styrene）、乙酸乙酯（Ethyl Acetate）、乙酸正丁酯（n-Butyl Acetate）、四氯乙烯（Tetrachloroethylene）、甲基異丁酮（Methyl Isobutyl Ketone）六種化合物標準氣體，以評估Tenax-TA被動式採樣熱脫附分析方法之被動式採樣率（Uptake rate）、方法準確度與精密度。所產生的標準氣體以偵檢器及活性碳管主動式採樣溶劑脫附方法確認濃度。分別使用250C、80%R.H.之200 ppm 乙酸乙酯、150 ppm 乙酸正丁酯、50 ppm 苯乙烯、100 ppm對──二甲苯、50 ppm 甲基異丁酮及 100 ppm 四氯乙烯之蒸氣，評佔各化合物以Tenax-TA熱脫附管加上擴散蓋於採樣時間0.5、1、2、4及8小時之被動式採樣率，測試樣品數各為7。並以250C、80%R.H.之標準氣體，評佔Tenax-TA熱脫附管加上擴散蓋於 0.1、0.5及1 倍空氣容許濃度之精密度與準確度，採樣時間4小時，測試樣品數各為7。結果顯示，Tenax-TA被動式採樣方法具有極佳精密度，平均變異係數為 1.6%~2.4%o然被動式採樣率會隨採樣時間增加而降低。本研究側得0.5小時至4小時之時間加權平均被動式採樣率如下：乙酸乙酯，1.61 ng ppm-1min-1；乙酸正丁酯，2.06 ng ppm-1min-1； 苯乙烯，3.28 ng ppm-1min-1；對──二甲苯，2.59 ng ppm-1min-1；甲基異丁酮，1.76 ng ppm-1min-1：四氯乙烯，3.00 ng ppm-1min-1。其中苯乙烯及對──二甲苯之被動式採樣率與 MDHS 80提供之數值2.0 ng ppm-1min-1及1.82 ng ppm-1min-1，差異頗大。對於此六種有機溶劑，Tenax-TA被動式採樣熱脫附分析方法之整體不確定性（overall uncertainty）小於25％。鑑於被動式採樣率在採樣時間0.5小時至1小時之間明顯下降；於作業現場應用此被動式採樣率，採樣時間最好能大於1小時且小於4小時。

This study aims to evaluate uptake rates of Tenax-TA passive sampler using dynamically generated known concentration vapor of p-xylene, styrene, ethyl acetate, n-butyl acetate, tetrachloroethylene, and raethyl isobutyl ketone. Calibrated detector and pumped charcoal tube confirmed the concentration of generated vapor. The uptake rates of Tenax-TA passive sampler were evaluated at 25~C, 80% R.H. by 200 ppm ethyl acetate, 150 ppm n-butyl acetate, 50 ppm styrene, 100 ppm p-xylene, 50 ppm methyl isobutyl ketone and 100 ppm tetrachloroethylene individually, for half an hour, one, two, four and eight hour sampling. Accuracy and precision of Tenax-TA passive sampling with thermal desorption method were evaluated by 0.1, 0.5 and 1 times of permissible exposure limit of tested compound for four hour samplings with seven replicates. The average coefficients of variation are between 1.6% and 2.4% for the tested solvents. The precision is excellent, however, the uptake rate decreases with the increaseof sampling time. The four-hour time-weighted-average uptake rates for ethyl acetate, n-butyl acetate, styrene, p-xylene, methyl isobutyl ketone and tetrachloroethylene are 1.61, 2.06, 3.28, 2.59, 1.76 and 3.00 ng ppm-1min-1, respectively. The uptake rates of styrene and p-xylene are quite different from 2.0 and 1.82 ng ppm-1min-1 suggested by MDHS 80. The overall uncertainties of Tenax-TA passive sampler for the six solvents are less than 25%. Owing to the sharp decrease of uptake rate between half an hour and one-hour sampling, a minimum of one hour and less than eight hour sampling is recommended for field sampling.